The present invention relates to a seat-back frame and a vehicle seat, and particularly to a seat-back frame and a vehicle seat that reduces an impactive shock that would otherwise be applied to a neck portion upon a rear-end collision.
Conventionally, upon so-called rear-end collision, such as a collision against a rear portion of a vehicle, and collision of a vehicle during rearward movement thereof, it is likely that a head portion of a seating occupant is suddenly tilted rearward due to inertial movement so that a neck portion of the occupant is likely to be subjected to an impactive shock.
Thus, seats for vehicles such as automobiles are each provided with a headrest located above a seat-back and configured to receive a head portion of an occupant from the rearward, so as to protect the head portion, a neck portion, and the like of the occupant, and to mitigate an impact against the head portion upon rear-end collision.
However, even with the provision of the headrest, it is sometimes impossible to sufficiently mitigate an impactive shock to be otherwise applied to the neck portion of the occupant, unless a gap between the head portion of the occupant and the headrest is quickly reduced upon rear-end collision.
To solve such a problem, there has been proposed such a seat-back configured to rearwardly move an occupant upon rear-end collision, and to forwardly operate a headrest by this movement load to support a head portion of the occupant, thereby mitigating an impactive shock that would otherwise be applied to a neck portion of the occupant (see Japanese unexamined patent publication no. JP2003-341402A (“the '402 Publication”), for example).
Further, there has been known such a technique in a vehicle seat configured to include a seat-back having a seat-back frame for supporting a seat-back cushion, wherein a region of the seat-back, to which a chest portion (herein defined as an upper torso portion) of an occupant abuts upon rear end collision, is rendered to have a smaller spring coefficient and a larger damping coefficient than other regions (see Japanese unexamined patent publication no. JP2005-028956A (“the '956 Publication”), for example).
The technique disclosed in the '402 Publication is configured to receive a rearward movement of the chest portion of the occupant upon rear-end collision by a pressure receiving member, and to forwardly move the headrest interlockedly with a rearward movement of the pressure receiving member. However, the technique is configured such that a part of energy of the rearward movement of the occupant upon rear-end collision is consumed for the forward movement of the headrest, thereby disadvantageously making it difficult to substantially increase a sinking amount of the occupant into a seat cushion. It is further required to separately provide a mechanism for moving the headrest, thereby disadvantageously increasing the cost of the seat.
In turn, the technique disclosed in the '956 Publication is configured: to reduce the spring coefficient of the region, to which the chest portion of the occupant abuts, to increase a rearward displacement of the chest portion, thereby decreasing a relative displacement between the head portion and the chest portion; and to increase the damping coefficient, to thereby restrict a rebound of the chest portion so as to reduce a relative speed between the head portion and chest portion, thereby reducing a shearing force acting on the neck portion. However, this rather makes it difficult to hold a posture by the pressure receiving member, thereby disadvantageously making it difficult to simultaneously establish a posture holding and a seating feeling.
In this respect, according to a technique to mount the pressure receiving member to the seat frame by a wire for posture holding, the wire would be stiff and obstruct sinking to make it difficult to increase a displacement of sinking, thereby disadvantageously making it difficult to simultaneously establish the increased displacement and the seating feeling.